Electric spark ignition apparatus



Oct. 13, 1953 J. A. LAIRD ELECTRIC SPARK IGNITION APPARATUS Filed July 16, 1951 Fig.1

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Patented Oct. 13, 1953 smc'rmo spam; IGNITION arraaa'rvs v John Andrew Laird, Coventry, England, assignor Birming to Joseph Lucas Limited, land MEIIP.

Application July 16, 1951, Serial N0. 235,966 In Great Britain July 20, 1950 7 Claims. 1

This invention relates to electric spark ignition apparatus of the kind which includes a condenser for effecting a relatively large discharge across an ignition gap in an internal combustion prime mover, and particularly an ignition gap of the so-called low voltage type in which a semi-conductive path is provided between the gap elec- The object of the invention is to provide an eflective and reliable apparatus in a simple form.

The invention comprises the combination of charging means, a resistance'in series with the charging means, and a control gap in parallel with the resistance, the latter being adapted for connection to an ignition gap, the necessary capacity being provided by either the self-capacity of the charging means and/or the associated conductors, or by a separate condenser connected in parallel with the-charging means.

In the accompanying diagrams:

Figures 1 and 2 illustrate two embodiments of the invention.

Referring to Figure 1, thereis provided an induction coil comprising primary and secondary windings a, b, the primary winding being energised from a battery or other direct current source through a rotary interrupter c, across which latter may be connected the usual sparksuppressing condenser d. In parallel with the secondary winding b or the coil may be connected the condenser e to be charged by the coil. Where the self or distributed capacity of the coil and/or the conductors connected thereto is adequate the condenser 6 need not be provided, or alternatively the required capacity may be provided in part by the self or distributed capacity and an additional condenser. If desired the coil may be connected to the condenser through a rectifier as indicated by f in Figure 2. In series with one end of the secondary winding b and at a position beyond the condenser is connected a resistance a of any appropriate value, for example, 0.5 megohm. Also in parallel with the resistance (and rectifier when used) is provided a circuit containing the control gap h. The resistance g may be connected directly to the ignition gap 1, but preferably a gap 1' is provided betwen the resistance and the ignition gap. It is also advanta geous to insert an inductance (as k Figure 2) in any convenient position to control the rate of discharge of the condenser.

The arrangement is such that the first effect of an impulse from the induction coil is to break down the ignition gap i, or both the ignition gap Later when the potential difference across the ends of the resistance a rises to a sufllcient amount the control gap h breaks down and allows the charge stored in the condenser by the previous impulse to discharge across this gap. After the discharge across the ignition gap has ceased, the residual energy of the coil serves to re-charge the condenser.

Figure 2 illustrates the application of the invention to a system which includes a plurality of ignition gaps, as in a 4-cylinder engine, where each gap in turn is connected to the system through a distributor comprising a rotary arm m. and an arrangement of stationary electrodes 11., the gap 1 above mentioned being provided between the arm and each of the adjacent elecclaim as new and desire to secure by Letters Patent is:

1. Electric spark ignition apparatus comprising, in combination, charging means having a circuit connected to an ignition gap adapted to break down upon the initial charging impulse of said means, a resistance in' series with said circuit, capacity included in the circuit adapted to store energy therein, and a control gap connected in parallel with said resistance and adapted to break down at a higher potential than the breakdown potential of the ignition gap when the potential across the resistance rises to an appropriate value due to flow of current in the circuit following the initial breakdown of the ignition gap, whereby the stored energy in the and the series gapj (when the latter is provided). break down upon the initial charging impulse.

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